salexes wrote:I changed my ISP from Telekom to Vodafone and now I only have an IPv6 and IPv4 is dual-stack lite.

Complain with your new ISP and ask for a public IPv4 address as this is not workable for "calling home" applications from the many IPv4-only sites.

salexes wrote:I tried everything to get myQNAPcloud working again but without success. How to I need to configure it to make it work again ?

That "myQNAPcloud" a little bit to generic - myQNAPcloud CloudLink is certainly workable. However other applications requiring IPv4 connections and port forwarding like [yournasname].myqnapcloud.com DDNS based connection, to the NAS, for QVPN, ... will never work without a public routable IPv4 on your Internet connection.